Cytology of Interspecific Hybrids in Section Arachis of Peanuts1

Abstract

Abstract Interspecific hybrids between Avachis correntina (Burk.) Krap. et Greg. nom. nud. (coll. GKP 9530–31) and seven other diploid peanut species of section Arachis nom. nud. [syn. Axonomorphae (7)] were cytologically analyzed. Although hybrid plants were partially sterile, cytological barriers to gene exchange were nonexistent except for A. batizocoi Krap. et Greg, hybrids. Arachis batizocoi hybrids had between 0 and 4.67% pollen fertility, probably due to an average of 2.88 univalents per cell. Laggards and anaphase I bridges were observed in 85% of the hybrid cells. Because the cultigen, A. hypogaea L. (2n = 40), and the diploid wild species (2n = 20) are at different ploidy levels, hybridization results in sterile triploid plants. This is a major barrier to introgression from wild to cultivated varieties. In order to derive wild species of section Arachis at the same ploidy level as A. hypogaea, 572 three to six-day-old seedlings were colchicine-treated representing 34 interspecific Arachis section hybrid combinations. Eighty-one cytologically confirmed amphidiploids plus 49 probable ones based on plant morphology were isolated. After colchicine treatments, 26 autotetraploids were likewise produced from six species. The observations indicated that selection can occur at the diploid level in wild species for desired agronomic traits or for disease and insect resistances. Colchicine-treated selected hybrid seedlings would then serve as a pathway for overcoming the major sterility obstacle to introgressing germplasm into A. hypogaea.